Research Guides: Evidence Based Practice: 2. Align: Levels of Evidence

Align: Levels of Evidence

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Study designs are placed into a hierarchy based on their reliability (probability of bias) known as the Levels of Evidence.

The Levels of Evidence are often represented by a pyramid, with the highest levels of evidence (least common) near the top, and the lowest levels of evidence (most common) near the bottom. The pyramid above is based on the Oxford Centre for Evidence Based Medicine's rating system for therapeutic studies, but a variety of rating systems exist.

Types of Study Design:

Systematic Reviews & Meta-Analysis
Double-Blind & Randomized Controlled Trials
Cohort Studies
Case-Control Studies
Case Series & Case Reports

Introduction to Study Design
Defines types of study designs and explains what to look for when reading research to determine the study design.
The Well-Built, Patient-Oriented Clinical Question
Use this worksheet to break down the parts of your PICO question.

Question Type & Study Design

Some study designs are better suited to answer certain types of questions. Identifying the clinical domain your question falls under can help determine what study designs to look for in order to find the best, most suitable evidence. Systematic Reviews and Meta-Analyses are always preferred.

Check off the clinical domain and preferred study design type on the Well-Built, Patient-Oriented Clinical Question worksheet. The link to that worksheet can be found above.

Clinical Domain	Preferred Study Design (after systematic reviews and meta-analyses)
Cost-Effectiveness	Economic Analysis
Diagnosis	Cross-Sectional Studies or Gold Standard
Etiology or Prognosis	Cohort > Case-Control > Case Series
Prevention	Randomized Controlled Trial > Controlled Trial > Cohort > Case-Control
Quality of Life	Qualitative Studies
Therapy	Randomized Controlled Trial > Controlled Trial or Quasi-Experimental Studies

For example:

Clinical question: In adult patients with total hip replacements, how effective is pain medication compared to aerobic stretching in controlling post operative pain during the perioperative and recovery time?

Clinical domain: Therapy

Preferred study designs: Systematic Reviews, Meta-Analyses, Randomized Controlled Trials, and Controlled Trials

Click "Next" to learn about the Acquire Step.